1. Field of the Invention
The present general inventive concept relates to a symbol timing recovery apparatus used with a vestigial side band (VSB)-type receiver, and a method of using the same. More particularly, the present general inventive concept relates to a symbol timing recovery apparatus used with a vestigial side band (VSB)-type receiver, capable of efficiently performing symbol timing recovery using a lower band, and a method of using the same.
2. Description of the Related Art
When demodulating data in a receiver which receives data transmitted through a vestigial side band (VSB) scheme, the same clock as used in a transmitter should be generated. This process is called ‘Symbol Timing Recovery.’
The symbol timing recovery may be performed by a method which uses a data segment synchronizing signal regularly inserted during data transmission by the transmitter or by a method which uses a band edge component maximization (BECM) algorithm.
The BECM algorithm recovers symbol timing by reading phase information of a received signal using a spectral line which is a harmonic signal of an upper frequency band signal of a VSB-modulated received signal. A Gardener algorithm is a typical example of the BECM algorithm.
FIG. 1 is a block diagram of a symbol timing recovery apparatus according to a conventional BECM algorithm.
Referring to FIG. 1, the conventional recovery apparatus 100 comprises an analog-to-digital converter (ADC) 101, a mixer 103, a matched filter 104, a BECM 200, a loop filter 109, and a numerically controlled oscillator (NCO) 111.
The VSB-modulated received signal is converted to a digital signal by the ADC 101. The mixer 103 receives a second NCO signal and converts the digitalized VSB signal to a base-band signal.
From a signal filtered off by the matched filter 105, the BECM 200 outputs error information of a symbol clock. The loop filter 109 outputs NCO controlling voltage corresponding to the error information, thereby adjusting the symbol clock input to the ADC 101.
FIG. 2 is a block diagram illustrating the BECM of FIG. 1. Referring to FIG. 2, the BECM 200 comprises a pre filter 201, a non-linear device 203, a symbol tone extractor 205, and a phase detector 207.
The pre filter 201 receives the VSB-modulated signal, which is passed through the matched filter 105 (FIG. 1), and filters off only the upper frequency band signal. The non-linear device 203 generates harmonic components of the signal output from the pre filter 201. The symbol tone extractor 205 extracts symbol tone from the plurality of harmonics generated by the non-linear device 203. The symbol tone refers to a component having the same frequency as the clock used in the transmitter. The phase detector 207 outputs the error information of a symbol clock (or, symbol phase), which is the information on the error between a preset reference symbol phase and a phase of the extracted symbol tone.
As aforementioned, the symbol timing recovery apparatus using the conventional BECM algorithm uses only the upper frequency band of the received VSB-modulated signals.
However, when the received VSB-modulated signals are distorted on the transmission channel and the signals in the upper frequency band are seriously damaged, performance of the symbol timing recovery apparatus is considerably deteriorated. The damage rate of the upper frequency band signals increases especially in an environment having lots of multi-path components, and this causes deterioration of receiving performance.